1. Field of the Invention
The present invention relates generally to integrated circuits and a method of manufacturing the same, and more particularly, to a semiconductor device that has a dielectric structure capable of enhancing electrical characteristics, and a method of manufacturing the same.
2. Description of the Related Art
The increasing integration density of semiconductor devices needs a capacitor of a DRAM having greater capacitance per unit area. To meet this requirement, a variety of methods have been introduced. Such methods include a method of increasing the electrode surface area of the capacitor by forming a three-dimensional stacked, cylindrical, or trench type electrode or by forming hemispherical grains on the electrode surface, a method of thinning a dielectric layer, a method of forming the dielectric layer using of high-dielectric material having a high dielectric constant or a ferroelectric material and so on. However, the above methods are not without their limitations. For example, reducing the thickness of the dielectric layer seriously increases leakage current as the capacitance increases. When a material having a high dielectric constant, for example, Ta2O5 or BST((Ba,Sr)TiO3), is used for the dielectric layer, polysilicon, which has been conventionally used to form the electrode, cannot be used. This is because the use of the polysilicon causes tunneling and increases leakage current when the thickness of the dielectric layer is reduced.
As another method for increasing capacitance per unit area of the capacitor, a metal-insulator-metal (MIM) capacitor whose electrode is formed of, instead of polysilicon, a metal having a large work function, such as TiN or Pt, has been suggested. In this method, the growth of a native oxide layer on the metal electrode is suppressed to prevent a capacitance reduction by a low-dielectric oxide layer. In the MIM capacitor, an oxide of a metal having a great affinity for oxygen is mostly used for a dielectric layer.
Recently, in order to resolve problems caused by increase in leakage current with reduced thickness of the dielectric layer, forming a composite dielectric layer, which includes a conventional dielectric layer and a higher dielectric constant layer, instead of a single dielectric layer, has been suggested. The formation of the composite dielectric layer prevents leakage current from increasing due to the use of the higher dielectric constant layer, without reducing capacitance, and improves the electrical properties of the capacitor.
a needs still exists for Particularly, a great deal of research has been conducted into a dual or multi-dielectric layer including a Al2O3 layer, which has a small dielectric constant of about 10 but effectively prevents leakage current, and an HfO2 layer, which has a large dielectric constant of 20-25 and effectively prevents leakage current due to its large band gap.